1. Field of the Invention
This invention relates to the field of video compression systems, and in particular to programmable DVD video encoders.
2. Description of the Related Art
A video program signal is converted to a digital format, and then compressed and encoded in accordance with one of several known compression algorithms or methodologies. This compressed digital system signal, or bitstream, which includes a video portion, an audio portion, and other informational portion, is then transmitted to a receiver. Transmission may be over existing television channels, cable television channels, satellite communications channels, and the like. A decoder is then typically employed at the receiver to decompress and decode the received system signal in accordance with the same compression algorithm used to encode the signal. The decoded video information may then be output to a display device, such as a television (TV) monitor.
Video compression and encoding is typically performed by a video encoder. The video encoder normally produces a compressed digital system signal that conforms to a recognized standard or specification agreed to among the senders and receivers of digital video signals. One such standard is DVD. It includes audio and video compression technologies, as well as provisions for other information streams. The video compression standard adopted by DVD was developed by the Moving Pictures Experts Group (MPEG). The MPEG standard concerns high-quality coding of possibly interlaced video, including high definition television (HDTV). A wide range of applications, bit rates, resolutions, signal qualities and services are addressed, including all forms of digital storage media, TV broadcasting and communications.
The MPEG standard, although it details the structure and syntax of the compressed bitstreams, does not provide complete system specifications. A nearly infinite number of bitstreams can be generated to represent an image sequence while conforming to the MPEG standard. Design considerations such as image preprocessing, motion estimation methods, the order of compressed frame types, bit-rate management, implementation complexity, coded image size, color space sampling, and field interleaving, all lead to different representations of the same image. It should be recognized that the different representations may have varying degrees of quality, both in terms of compression and accuracy, but they all conform to the MPEG standard. A somewhat lesser degree of freedom exists in the way a bitstream is decoded, but nevertheless exists. For example, note that some video degradation might be an acceptable tradeoff for reduced implementation complexity, or that the coded image characteristics (size, frame rate) might be incompatible with the display device and require some adjustments (scaling, pulldown). The MPEG standard carefully avoids addressing issues such as these, preferring instead to allow industries to "customize" encoder and decoder implementations to their best advantage.
Currently, the customization of the encoder and decoder implementations is performed by the system designers, primarily with a combination of hardware and proprietary microcode, and the displayed image quality thereby determined. One drawback of this approach is that the digital media vendors cannot easily "improve" image quality to distinguish themselves from their competitors, nor can they easily upgrade their systems to incorporate the latest compression advances. It is desirable to provide a method for DVD media vendors to participate in the encoder and decoder customization process to produce media classes that provide for optimized trade-offs (e.g. capacity vs. image quality), and in so doing provide better performances for specific applications.